Android 7.1.2源码之修改开机动画

  开机动画是Android系统的UI启动过程中的动画显示，在UI启动完成，看到桌面或者锁屏界面出现后，自动结束。对开机动画的定制比较简单，制作图片就可以完成。开机动画执行者代码路径为：frameworks/base/cmds/bootanimation。它将生成本地程序bootanimation，被init通过init.rc启动。

开机动画的两种内容：

  1. zip包。
    /system/media/bootanimation-encrypted.zip
    /system/media/bootanimation.zip
    /oem/media/bootanimation.zip
    以上任意一种，放置OK后，重新make生成img。
  2. 默认动画。
    默认动画是资源包中的资产文件，路径为：frameworks/base/core/res/assets/images。默认动画的两个文件为android-logo-mask.png和andriod-logo-shine.png。
    默认动画的运行逻辑是：有透明区域mask文件放在上面，shine文件放在下面水平方向移动。这两个文件可以被替换实现定制。
    优先使用的是特定格式的zip包，如果不能成功，则使用默认的动画。至于bootanimation.zip里边的格式，很多书或者帖子都有讲，感觉不是很全，下面贴上源码中的格式。

bootanimation format

zipfile paths

The system selects a boot animation zipfile from the following locations, in order:

/system/media/bootanimation-encrypted.zip (if getprop("vold.decrypt") = '1')
/system/media/bootanimation.zip
/oem/media/bootanimation.zip

zipfile layout

The bootanimation.zip archive file includes:

desc.txt - a text file
part0  \
part1   \  directories full of PNG frames
...     /
partN  /

desc.txt format

The first line defines the general parameters of the animation:

WIDTH HEIGHT FPS
  • WIDTH: animation width (pixels)
  • HEIGHT: animation height (pixels)
  • FPS: frames per second, e.g. 60

It is followed by a number of rows of the form:

TYPE COUNT PAUSE PATH [#RGBHEX CLOCK]
  • TYPE: a single char indicating what type of animation segment this is:
    • p – this part will play unless interrupted by the end of the boot
    • c – this part will play to completion, no matter what
  • COUNT: how many times to play the animation, or 0 to loop forever until boot is complete
  • PAUSE: number of FRAMES to delay after this part ends
  • PATH: directory in which to find the frames for this part (e.g. part0)
  • RGBHEX: (OPTIONAL) a background color, specified as #RRGGBB
  • CLOCK: (OPTIONAL) the y-coordinate at which to draw the current time (for watches)

There is also a special TYPE, $SYSTEM, that loads /system/media/bootanimation.zip
and plays that.

loading and playing frames

Each part is scanned and loaded directly from the zip archive. Within a part directory, every file
(except trim.txt and audio.wav; see next sections) is expected to be a PNG file that represents
one frame in that part (at the specified resolution). For this reason it is important that frames be
named sequentially (e.g. part000.png, part001.png, …) and added to the zip archive in that
order.

trim.txt

To save on memory, textures may be trimmed by their background color. trim.txt sequentially lists
the trim output for each frame in its directory, so the frames may be properly positioned.
Output should be of the form: WxH+X+Y. Example:

713x165+388+914
708x152+388+912
707x139+388+911
649x92+388+910

If the file is not present, each frame is assumed to be the same size as the animation.

audio.wav

Each part may optionally play a wav sample when it starts. To enable this, add a file
with the name audio.wav in the part directory.

exiting

The system will end the boot animation (first completing any incomplete or even entirely unplayed
parts that are of type c) when the system is finished booting. (This is accomplished by setting
the system property service.bootanim.exit to a nonzero string.)

protips

PNG compression

Use zopflipng if you have it, otherwise pngcrush will do. e.g.:

for fn in *.png ; do
    zopflipng -m ${fn}s ${fn}s.new && mv -f ${fn}s.new ${fn}
    # or: pngcrush -q ....
done

Some animations benefit from being reduced to 256 colors:

pngquant --force --ext .png *.png
# alternatively: mogrify -colors 256 anim-tmp/*/*.png

creating the ZIP archive

cd <path-to-pieces>
zip -0qry -i \*.txt \*.png \*.wav @ ../bootanimation.zip *.txt part*

Note that the ZIP archive is not actually compressed! The PNG files are already as compressed
as they can reasonably get, and there is unlikely to be any redundancy between files.